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The World


             The Fathomless Abyss is a cylinder that is usually closed at the top, and has no bottom. It is literally a bottomless pit. The cylinder is a mile in diameter. The walls appear to be natural, as though the pit is a cave that shows evidence of a variety of means of formation, confounding those with a detailed knowledge of geology. There is ample evidence that it was a lava tube, but likewise there’s evidence to show that it was carved by rushing water, pulled open by geologic faults, and so on. From a purely scientific standpoint it utterly defies classification.

There are both naturally occurring and manmade ledges at various places along the pit, some big enough to support decent-sized camps, or even mini-villages. But at no point has anyone ever seen the pit less than half a mile or more than a mile across.

Caves appear along the walls at random spots, and these are more easily classified in terms of their creation. Some are clearly lava tubes, others cut by water, etc. Many of them are manmade tunnels. The natural caves twist and turn back into solid bedrock, but always eventually dead end no more than a couple miles from the pit itself. Many of these caves are big enough to house entire villages.

There are veins of various precious metals, gemstones, and even petroleum and natural gas all along the endless length of the pit. Those who can find, secure, and exploit these deposits rank among the wealthiest of the captive population, but doing all three of those things with any reliability is no easy feat.

Occasional waterfalls tumble out of cave mouths to fall forever downward. These are the primary sources of fresh water for residents of the pit. Other pools of fresh water are found here and there a short distance into some caves. Waterfalls are a little strange in the physics of a bottomless pit. The farther down the length of the waterfall you go the more diffuse the water, so eventually it just feels like it’s raining, farther below, a light sprinkle, farther still and the water has dissipated into a layer of fine mist. Below the mist layer, it’s dry.

Much more dangerous than the waterfalls are the occasional lava tubes that spill molten rock down the side of the pit. More than one unlucky village has fallen victim to these unpredictable disasters.

Throughout most of the pit, it smells pretty much as one would expect a cave to smell, a little dusty—a rocky, chalky smell—but various patches of moss and other vegetation can bring a more loamy tinge to the air.

Despite various concerted efforts over a thousand of years, and despite the assertion of various clerics and charlatans, no one has yet determined anything approaching a pattern for when or where the pit will open next, and no one has shown any real evidence that it’s ever opened in the same place twice—at least at the same time.



Why don’t they just tunnel out? People have tried that over the centuries but no matter how long they keep digging and how sure they are that they’re digging in a straight line out from the pit wall, they end up looping back, eventually emerging back into the pit at some strange distance up or down that makes no sense to anyone looking at it from inside the tunnel. There is no way out except when the top of the pit opens to some strange new world and time.

Though there’s no way to dig yourself out, once you break through back into the pit, these man-made tunnels  can be used to move up and down the pit safer and more quickly. Control of two-ended tunnels, especially if they connect places of particular interest, have considerable value, both strategically and economically, especially since there’s no way to reliably create new tunnels—they always end up opening somewhere you least expect, though always back in the pit itself. Excess dirt from tunneling tends to just be tossed down the pit, but is also used for building materials.

The Crown

When the pit closes, what appears is in every way the ceiling of a natural cave, replete with stalactites and so on. Locals call this the Crown.

Efforts to dig up out of the pit have always just gone up and up without actually getting out. When the pit opens, anyone unfortunate enough to be in one of those tunnels appears in thin air however high up they’ve managed to dig, and they fall back into the pit.

When the Crown closes again, the ceiling is restored to its default position in every way, with no sign of any excavation or anything else. Even if you just secure a bolt from the ceiling to hang things over the pit, when the Crown opens, that bolt is just hanging in thin air and it, and whatever’s attached to it, immediately falls back into the pit.

The top 2-10 miles of the pit, near the Crown, is a no man’s land called the Smog where the smoke of fires below accumulates, and only belches out when the Crown opens into a new world. The closer you are to the Crown, the more smoke has accumulated.





The interior environment of the pit is comfortable for human life, with an Earthlike atmosphere and normal pressure and gravity. But that means if you fall, you keep falling. If nothing manages to stop you, you fall and fall and fall, literally forever.

There are no discernable seasons. It’s always pretty much the same in there, maybe 70°F or so. “Rain” would only be encountered near the bottom of waterfalls, but waterfalls also provide a humidity that helps certain species of plant life thrive.


The Sunstrip


The pit has a strange day/night cycle provided by the Sunstrip. This is a thin line of brilliant light with all the properties of sunlight that slowly fades into and out of existence on a roughly 24-hour cycle. It appears as a line of light, almost like the filament of an incandescent light bulb that slowly fades up to reach a peak luminosity at “noon,” then slowly fades back down, disappearing entirely at “midnight.” Humans will experience essentially complete darkness for about three hours on either side of midnight, but other creatures with better low-light vision will continue to benefit from the Sunstrip’s weaker illumination up to the hour or so before and after midnight, during which complete darkness reigns.

The Sunstrip provides enough UV light for photosynthesis, and heat enough to account for the pit’s constant temperature through—as far as anyone knows—its entire length. Because the Sunstrip fades in and out equally along its entire length, there are no “time zones” in the Abyss. If it’s noon in one place, it’s noon everywhere.

With a diameter of only a mile, and the Sunstrip forming the perfect center of the circle, the Sunstrip doesn’t have to get nearly as hot as the sun in order to keep the interior at a more-or-less constant temperature. Still, especially at high noon, it’s going to be way too hot to touch, and bright enough that not only can’t you look directly at it but it’ll effectively block your view of the other side of the pit.

For this reason, high noon can be as uncomfortable for most of the pit’s inhabitants as midnight. People tend to live their lives in the more comfortable twilight periods.




The pit occasionally opens into onto a Void World—a planet without atmosphere—and when that happens the air rushes up like in a hurricane. Everyone must batten down against the wind for a time, and just like on Earth, hurricanes can cause considerable havoc. But at the same time, hurricanes have a beneficial cleansing effect on the pit, pulling out weak plants, and thoroughly clearing the Smog that has accumulated near the Crown. This is a rare event that might happen once every three generations. Younger Abyssals may not even really believe in hurricanes. Trading families know, however, that when the pit opens to a rushing upward gust that no one should traverse out of the open Crown, for no one ever returns from Void Worlds.

The Fathomless Abyss has an infinite supply of air at one atmosphere, so even when you open one end to a vacuum and it starts to rush out., the supply of air is infinite, so the pit just keeps throwing more air out until the Crown closes again, at which point the air inside quickly re-equalizes and everybody’s fine.






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